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tiistai 13. helmikuuta 2018 6.40.38 UTC+2 WB kirjoitti:
On Monday, February 12, 2018 at 10:07:11 PM UTC-6, Jonathan St. Cloud wrote:
No, and spectra is way too expensive to use for deck lids, fenders... It is in a lay up.
On Monday, February 12, 2018 at 5:44:57 PM UTC-8, Tony wrote:
You mean the tethers that keep deck lids, fenders, and the like from flying into the crowd?

Probably not needed in typical Sailplane crashes...

Spectra is a brand name for aramid fibers better know by another name: kevlar. I believe kevlar is used in the cockpits of the "safety cockpit" Schleicher gliders and probably others. A mix of carbon/kevlar seems to be common in the seatpans of new gliders these days.

Carbon shatters to (sharp) pieces, with wowen kevlar fibers in fabric the structure does not completely disappear around you in case of crash. AFAIK carbon itself is stronger fibre that kevlar. I think most flaps and ailerons are made of 100% kevlar, though not sure why. Maybe it's lighter than carbon and still strong enough?

On Mon, 12 Feb 2018 20:52:28 -0800, Jonathan St. Cloud wrote:
Interesting, as in sailing we have kevlar sails, but spectra lines.

Yes, and that 'Spectra' is a high density polyethylene, not aramid. I
used to use it as towline for F1A free flight competition models.

About 3-4 years ago my gliding club started to use it on our winches. Its
much better than steel cable: less stretch/energy storage and light
enough that two people can easily pull the end back to the launch point
if a launch was abandoned during the ground run.

On Tue, 13 Feb 2018 02:59:34 -0800, krasw wrote:
Carbon shatters to (sharp) pieces, with wowen kevlar fibers in fabric
the structure does not completely disappear around you in case of crash.
AFAIK carbon itself is stronger fibre that kevlar. I think most flaps
and ailerons are made of 100% kevlar, though not sure why. Maybe it's
lighter than carbon and still strong enough?

I don't know whether its lighter than carbon, but its easier to get
lighter weight kevlar fabric than carbon (35 gsm vs 80gsm). Horrible
stuff to work with, though.

Or a piece of yarn taped to either side of the canopy.Â* You could go big
and use TWO of Bumper's MkIV yaws trings, of course they'd have to be
reprogrammed to act as AoA indicators.Â* Last time I checked the firmware
upgrade only cost $895 and I think you could get a quantity discount for
two.

On Tuesday, February 13, 2018 at 2:59:37 AM UTC-8, krasw wrote:
I think most flaps and ailerons are made of 100% kevlar, though not sure why. Maybe it's lighter than carbon and still strong enough?

It's all about making a control surface that is limber enough in bending so it can deflect up and down while hinged to a bent wing, while still having enough torsional stiffness to transmit motion while resisting flutter.

Think about an early ASW20 at 2g, with the wings bent up about 1.5m. Now imagine deflecting the flaperons up on the left side and down on the right side (left stick). Because the wings and the flaperon hinge path are curved, the left flaperon trailing edge is being shortened as if the surface is being bent aft at the tip. On the right side, the trailing edge is being stretched as if the surface is being bent forward at the tip.

With the flaperons made of carbon, the result would be a control surface so stiff in bending that at any appreciable load factor the stick would spring to the center and resist flaperon deflection. This could be quite dangerous, because for example it would resist the leveling of wings while in a spiral dive.

Waibel's team at Schleicher appears to have tried several construction methods for the ASW20 flaperons before settling on sandwich construction with skins made with 2oz Kevlar on each side of Rohacell core foam. They also refined the design of the trailing edge joint so that it required a minimum of bonding paste, which helps keep the bending stiffness to a minimum. This was just one of a huge series of detail refinements required to go from a design to a functional product.

If you come to one of our Akaflieg sessions (next one is probably in late March) I'll show you all of the complexities that go into making effective flaperons.

On Tuesday, February 13, 2018 at 3:20:37 PM UTC-5, Bob Kuykendall wrote:
On Tuesday, February 13, 2018 at 2:59:37 AM UTC-8, krasw wrote:
I think most flaps and ailerons are made of 100% kevlar, though not sure why. Maybe it's lighter than carbon and still strong enough?

It's all about making a control surface that is limber enough in bending so it can deflect up and down while hinged to a bent wing, while still having enough torsional stiffness to transmit motion while resisting flutter.

Think about an early ASW20 at 2g, with the wings bent up about 1.5m. Now imagine deflecting the flaperons up on the left side and down on the right side (left stick). Because the wings and the flaperon hinge path are curved, the left flaperon trailing edge is being shortened as if the surface is being bent aft at the tip. On the right side, the trailing edge is being stretched as if the surface is being bent forward at the tip.

With the flaperons made of carbon, the result would be a control surface so stiff in bending that at any appreciable load factor the stick would spring to the center and resist flaperon deflection. This could be quite dangerous, because for example it would resist the leveling of wings while in a spiral dive.

Waibel's team at Schleicher appears to have tried several construction methods for the ASW20 flaperons before settling on sandwich construction with skins made with 2oz Kevlar on each side of Rohacell core foam. They also refined the design of the trailing edge joint so that it required a minimum of bonding paste, which helps keep the bending stiffness to a minimum. This was just one of a huge series of detail refinements required to go from a design to a functional product.

If you come to one of our Akaflieg sessions (next one is probably in late March) I'll show you all of the complexities that go into making effective flaperons.

And after you figure out bending while maintaining torsional stiffness add in a solution that allows the flexible hinge to provide the required profile through the region. All this to improve on a mylar seal.
Not so easy
UH

On Tuesday, February 13, 2018 at 5:59:37 AM UTC-5, krasw wrote:
tiistai 13. helmikuuta 2018 6.40.38 UTC+2 WB kirjoitti:
On Monday, February 12, 2018 at 10:07:11 PM UTC-6, Jonathan St. Cloud wrote:
No, and spectra is way too expensive to use for deck lids, fenders... It is in a lay up.
On Monday, February 12, 2018 at 5:44:57 PM UTC-8, Tony wrote:
You mean the tethers that keep deck lids, fenders, and the like from flying into the crowd?

Probably not needed in typical Sailplane crashes...

Spectra is a brand name for aramid fibers better know by another name: kevlar. I believe kevlar is used in the cockpits of the "safety cockpit" Schleicher gliders and probably others. A mix of carbon/kevlar seems to be common in the seatpans of new gliders these days.

Carbon shatters to (sharp) pieces, with wowen kevlar fibers in fabric the structure does not completely disappear around you in case of crash. AFAIK carbon itself is stronger fibre that kevlar. I think most flaps and ailerons are made of 100% kevlar, though not sure why. Maybe it's lighter than carbon and still strong enough?

correct lighter, and still strong, but more expensive (i think). they pay for it on the controls because it reduce the amount of weight (also reduces space) needed to mass balance the controls.

On Friday, February 9, 2018 at 1:31:46 PM UTC-5, Jonathan St. Cloud wrote:
Was so tried of the hard deck discussion thought I would try a discussion of dreams. After seeing the vision of Elon Musk with his Falcon Heavy, I had to pinch myself. Those two boosters landing in sync..

What are some of the innovative, new technology, original thought, scifi dreams, would you like to see in a brand new glider design? Let your inter Elon Musk flow.

We have seen the New Ventus, the JS-3 (very innovative), Dianna 3. So far the South Africans have shown the most original thought.

If you were to design a glider what are your dreams?

18/21 or 15/18 meters

Sustainer, jet, electric, two stroke?

Light weight: I would love to be able to get to 7.5 pounds with a 220 lb pilot+chute and up to 12ish pounds wet. This might take new manufacturing methods and materials. Perhaps pre-preg, vacuum bagging...?

Pedestal mounted wing?

interesting idea about smaller battery and a generator for FES.

would also be nice to have harnesses that retract like in a car. so that they arent flopping all over the cockpit. they'd be easier to reach too.

speaking of cars... this is a little nuts, but, airbags? i've always thought that during a crash, you probably smack the **** out of your head.